In order to accommodate a high-pressure fluid, various shapes of pressure tanks have been developed and many patents thereof have been filed.
FIG. 1 shows a pressure tank according to the related art, wherein FIG. 1a is a spherical pressure tank. FIG. 1b is a cylindrical pressure tank. FIG. 1c is a lobed pressure tank, and FIG. 1d is a cellular pressure tank.
Efficiency of a tank may be determined by volume efficiency and material consumption ratio.
                    ξ        =                              V            tank                                V            prism                                              [                  Equation          ⁢                                          ⁢          1                ]            
ξ Vtank Vprism The above Equation 1 can obtain the volume efficiency. In the above Equation 1, represents the volume efficiency, represents the volume of the tank, and represents the volume of the smallest rectangular parallelepiped box-volume which fully surrounds the tank.
ξ The higher the value of, the larger the volume efficiency of the tank, which means better utilization of the practical space consumed by the tank.
                    η        =                                            V              material                                      V              stored                                ⁢                      p                          σ              a                                                          [                  Equation          ⁢                                          ⁢          2                ]            
η Vmaterial Vstored The above Equation 2 expresses the material consumption ratio. In the above Equation 2, represents the material consumption ratio, the represents the volume of the material utilized to manufacture the tank, and the represents the amount of a fluid that can be filled in the tank.
η The lower the value of, the smaller the amount of material configuring the tank of the same volume, which means better increase in the efficiency of the tank.
TABLE 1Type of Pressure Tank  ξ  =            V      tank              V      prism        η  =                    V        material                    V        stored              ⁢          p              σ        a            Sherical Type0.521.5Cylindrical Type0.781.73-2.0Lobe Type0.851.73-2.0Cellular Type<1.01.73-2.0
The above Table 1 represents the volume efficiency and the material consumption ratio of the tank according to the related art. It should be noted that the material ratios for cylindrical, lobe, and cellular tanks do not include the end enclosures such that the real material ratios will be somewhat higher than shown in the table.
As can be appreciated from the above Table 1, the cellular tank has the most efficient volume efficiency, and the cylindrical tank, the lobed tank, and the cellular tank have about similar material consumption ratios.
It is to be noted that the lobe tanks are made by combining and overlapping two or more cylindrical tanks, have an interior wall spanning between the intersection lines, and are normally capped with doubly curved end shells. Such designs are rather complicated and difficult to manufacture and significant bending occur in the tank walls. The cellular tank has high volume efficiency and is efficient in that it does not require increased plate thickness for large-capacity tanks; one may just increase the number of cells. However, the cellular tank cannot be easily manufactured due to a rather complicated shape; moreover, the end capping problem is a particular challenge.
In all tank cases where there are curved shells involved, i.e. spherical, cylindrical, lobe and cell tanks, it is very difficult if not impossible to design for complete double barrier of the exterior walls.